From fccad11716ed4117a9b9b654d7ac3391e5e707d8 Mon Sep 17 00:00:00 2001
From: Roman Khimov <roman@nspcc.ru>
Date: Tue, 23 Jun 2020 21:57:05 +0300
Subject: [PATCH] native: drop accounts with zero balance

They make no sense. Fixes preview2 testnet state problem:

file BlockStorage_100000/dump-block-70000.json: block 69935: state mismatch for key ffffffff1454a6cb279fbcedc66162ad4ad5d1d910202b92743e000000000000000000000005: Deleted vs Added
---
 pkg/core/native/native_gas.go  |  6 +++++-
 pkg/core/native/native_neo.go  |  6 +++++-
 pkg/core/native/native_nep5.go | 14 ++++++++++++--
 3 files changed, 22 insertions(+), 4 deletions(-)

diff --git a/pkg/core/native/native_gas.go b/pkg/core/native/native_gas.go
index 000f365d1..08683863a 100644
--- a/pkg/core/native/native_gas.go
+++ b/pkg/core/native/native_gas.go
@@ -58,7 +58,11 @@ func (g *GAS) increaseBalance(_ *interop.Context, _ util.Uint160, si *state.Stor
 		return errors.New("insufficient funds")
 	}
 	acc.Balance.Add(&acc.Balance, amount)
-	si.Value = acc.Bytes()
+	if acc.Balance.Sign() != 0 {
+		si.Value = acc.Bytes()
+	} else {
+		si.Value = nil
+	}
 	return nil
 }
 
diff --git a/pkg/core/native/native_neo.go b/pkg/core/native/native_neo.go
index fcd256137..55c119b3f 100644
--- a/pkg/core/native/native_neo.go
+++ b/pkg/core/native/native_neo.go
@@ -180,7 +180,11 @@ func (n *NEO) increaseBalance(ic *interop.Context, h util.Uint160, si *state.Sto
 		}
 	}
 	acc.Balance.Add(&acc.Balance, amount)
-	si.Value = acc.Bytes()
+	if acc.Balance.Sign() != 0 {
+		si.Value = acc.Bytes()
+	} else {
+		si.Value = nil
+	}
 	return nil
 }
 
diff --git a/pkg/core/native/native_nep5.go b/pkg/core/native/native_nep5.go
index 597a407e0..a1db0ee7d 100644
--- a/pkg/core/native/native_nep5.go
+++ b/pkg/core/native/native_nep5.go
@@ -180,7 +180,12 @@ func (c *nep5TokenNative) transfer(ic *interop.Context, from, to util.Uint160, a
 	if err := c.incBalance(ic, from, siFrom, inc); err != nil {
 		return err
 	}
-	if err := ic.DAO.PutStorageItem(c.ContractID, keyFrom, siFrom); err != nil {
+	if siFrom.Value == nil {
+		err = ic.DAO.DeleteStorageItem(c.ContractID, keyFrom)
+	} else {
+		err = ic.DAO.PutStorageItem(c.ContractID, keyFrom, siFrom)
+	}
+	if err != nil {
 		return err
 	}
 
@@ -193,7 +198,12 @@ func (c *nep5TokenNative) transfer(ic *interop.Context, from, to util.Uint160, a
 		if err := c.incBalance(ic, to, siTo, amount); err != nil {
 			return err
 		}
-		if err := ic.DAO.PutStorageItem(c.ContractID, keyTo, siTo); err != nil {
+		if siTo.Value == nil {
+			err = ic.DAO.DeleteStorageItem(c.ContractID, keyTo)
+		} else {
+			err = ic.DAO.PutStorageItem(c.ContractID, keyTo, siTo)
+		}
+		if err != nil {
 			return err
 		}
 	}